PC booted up from sleep mode, now it's lagging

Hey guys.
So, I got this problem. I was out in vacation for a week, and I left my computer in sleep mode. No problemo, right? But when I arrive home and start it up like normal, it boots up into the BIOS screen, and then displays the 'Resuming Windows' start-up. It took about 10 minutes to start, as opposed to my 15 second boot time before this happened. I didn't mind, until I started up Borderlands 2, which made my CPU usage widget go haywire and display 100% usage, and Borderlands 2 taking about 30 minutes to start. I then shut it off, cleaned the computer, applied thermal paste, and booted it up again. It's still laggy, and when I started up Google Chrome and Skype, it lagged considerably. I started an older game, Deus Ex, and it lagged considerably, and had choppy audio. I scratched my head, and thought that this wouldn't be an overheat problem because the moment I started up my computer when this happened, I checked the temperature and it was fine, 25 degrees Celsius, which was surprising due to the humidity of my country. (Note: All the games and processes would run smoothly before this happened) Updated my Catalyst drivers, and it still did this. It was really dusty when I cleaned it, but it still lagged after I had wiped and dusted it off. Most of the dust collected onto my V6GT CPU cooler.

Anyways, the only actions I took was cleaning it with pressurized air, and then applied thermal paste for good measure.

Here's my specs:
AMD Phenom II X4 960T Processor 3.01 GHz
4.00 GB RAM
AMD Radeon HD 6700 Series
Cooler Master V6GT